When Minnesota's 85,000 pheasant hunters take to the fields beginning Saturday, some may encounter public hunting grounds trampled this summer by cattle.

Not cud-chewing escapees from nearby farms, but cattle intentionally placed on public grasslands in hopes of mimicking the beneficial effects on wildlife habitat that herds of wild bison had on the landscape hundreds of years ago.

This year, about 13,000 acres of state wildlife management areas (WMA) were grazed, part of a new Department of Natural Resources program that eventually will be expanded to about 50,000 acres — less than 4 percent of the 1.4 million-acre WMA system. The U.S. Fish and Wildlife Service and The Nature Conservancy also are using grazing on about 20,000 acres in Minnesota as a tool to improve wildlife habitat.

Prairies need regular disturbance to remain lush, and fire, haying and grazing are used, sometimes in combination. But advocates say grazing can create a more diverse prairie, with a better mix of shorter grass, taller grass and more flowers, than burning or haying alone.

"Tall, heavy switch grass that pheasant hunters love to hunt provides excellent nesting habitat, but not brood-rearing habitat,'' said Neal Feeken, prairie recovery project coordinator for The Nature Conservancy. "The first thing a hen does is take her brood to thinner cover. Grazing removes dead thatch and creates open areas for new plants and forbs [flowers]. Pheasants like the seed heads and bugs that go along with the flowers. We do [grazing] for the broad diversity that it brings.''

Conservation grazing isn't new — it's been used for years. But it's gaining traction with the DNR, partly because the Legislature directed the agency to set up a program. It is expected to take several years before the state hits the 50,000-acre target. But while officials insist wildlife habitat improvements are the ultimate goal, some question not only grazing's benefits to the landscape but whether agricultural demands will eventually trump wildlife priorities on public hunting lands.

"I'm not a big fan of it at all,'' said Jim Cox of Cologne, who sits on the Lessard-Sams Outdoor Heritage Council, which has funded grazing projects. "It can do a lot of damage to wetlands, with the cattle tromping around and staying in one place.''

More important, Cox and others fear that once state lands are fenced, political pressure could put cattle on those wildlife lands more frequently, including when there is a drought, at the expense of wildlife.

"When push comes to shove, if the interest is agriculture vs. wildlife, you know who will win, and it won't be us,'' Cox said.

Said Feeken: "I think that is a valid concern. It will require vigilance on our part. Those grasslands aren't intended for grazing. It's just a management tool.''

Carmelita Nelson, DNR prairie grassland coordinator, said habitat improvement is the No. 1 goal. "If you don't disturb grassland, it will go to brushland and trees,'' she said. "We're trying to keep it open prairie.''

But Gary Anderson of Morris, a hunter and president of the local chapter of the Minnesota Deer Hunters Association, is a disbeliever. "When they graze these public lands, they ruin it for hunting,'' he said. "It's all mud and deep holes.''

The latest trend in grazing is occurring at the 2,800-acre Chippewa Prairie in western Minnesota, about half of which is state wildlife area and half owned by TNC. There patch-burn grazing occurred this summer.

"It's grazing driven by fire, meant to replicate disturbance factors that formed the prairies,'' said Dave Trauba, DNR Lac qui Parle area wildlife supervisor. Workers burned a 300- to 400- acre patch of that prairie last spring, which caused an immediate growth of new grasses, and then turned the cattle loose. Cattle tend to stay in the burned area because of the lush vegetation, and leave the rest of the prairie to grow thick and tall.

The idea is to burn a different area next year. It's a better and cheaper option than setting up temporary fencing to restrict cattle, he said.

Meanwhile, Trauba said, as part of the agreement the local cattle owner is idling his own 560-acre pasture of native prairie to invigorate it.

"The result is better wildlife habitat on his land and on ours,'' Trauba said.

Trauba and Feeken, both duck hunters, said cattle trample cattails, creating open water for waterfowl. "Many of our wetlands are being choked with cattails, and cattle can be a good tool to open them up,'' Feeken said.

Last spring was wet, and little prairie burning could be done, Nelson said. "Grazing is a great alternative,'' she said. "It's a really flexible tool.''

Trauba said officials are studying the impacts of patch-burn grazing to vegetation and wildlife, including bees and butterflies, and it will take several years to measure results.

"This is a big, bold venture,'' he said. "We have to give it some time before we can draw meaningful conclusions.''

Meanwhile, cattle should be off the public lands by the time pheasant hunters start hunting them Saturday.

Doug Smith • doug.smith@startribune.com